Enzymatic dehairing process

ABSTRACT

Process for dehairing skins and hides by treatment thereof, at a pH less than 5, with a mold-fungus protease showing its optimum effect at a pH below 5, with pepsin, with papain, or with a combination of these enzymes.

ite States Patent [72] Inventors R011 Monsheimer Darmstadt-Eberstadt; Ernst Pl'leiderer, Darmstadt-Arheilgen; Helmut Uhlig, Rossdorf/Darmstadt, all of Germany [21] Appl. No. 815,236

[22] Filed Apr. 10, 1969 [45] Patented Nov. 30, 1971 [73] Assignee Rohm Gesellschaft mit beschrenkter Haftung Darmstadt, Germany [32] Priority Apr. 13, 1968 3 3 Germany [54] ENZYMATIC DEHAIRING PROCESS 4 Claims, No Drawings [52] US. Cl 195/6 [51] 1nt.C1 C12b 1/00 [50] Field of Search... 195/6 [56] References Cited UNITED STATES PATENTS 2,289,937 7/1942 Pfannmuller 195/6 2,363,646 1 1/1944 Conquest et al. 195/6 2,480,761 8/1949 Mulqueen 195/6 Primary ExaminerA. Louis Monacell Assislan! ExaminerGary M. Nath AltorneyCurtis, Morris & Safford ABSTRACT: Process for dehairing skins and hides by treatment thereof, at a pH less than 5, with a mold-fungus protease showing its optimum effect at a pH below 5, with pepsin, with papain, or with a combination of these enzymes.

ENZYMATIC DEHAIRING PROCESS The present invention relates to processes for the enzymatic dehairing of skins and hides.

The enzymatic dehairing of skins and hides has up till now been carried out in a weakly acid to weakly alkaline region with proteolytic enzymes which exert their optimum effect within this region. These enzymes include the majority of enzymes obtained from mold fungi or bacterial cultures, as well as pancreatic enzymes. The known dehairing processes have the disadvantage that the undesired growth of bacteria and fungi in the dehairing bath must be hindered by preservatives. This precaution is critically necessary, particularly in tropical countries, and leads to a corresponding increase in the cost of the process.

A process for dehairing using proteolytic enzymes has now been found according to which skins and hides are treated under nonswelling conditions at pH values below 5 with proteolytic enzymes exhibiting their optimum effect at pH values below 5, and/or with pepsin, and/or with papain. The hair is subsequently removed.

Of the enzymes useful for the process, pepsin and papain are of particular importance. They can be used alone or together, optionally also in combination with other kinds of enzymes. For pepsin, the most favorable working region is between pH 3 and 5, and the optimum efficacy for the process of theinvention is observed at about pH 4. Papain is preferred in the pH region 4.0 to 5.0.

The enzyme bath should contain, for example, from 0.1 to 0.5 percent, calculated on the softened weight of the hides, of an enzyme product having an enzyme activity of 55,000-60,000 EZA. At a working temperature of 40 C., hair can be removed in from 24 to 48 hours.

[Enzyme activity, EZA, is determined using hemoglobin as a substrate. The substrate is prepared by suspending 4.6 grams of hemoglobin in 143.4 ml. of water. After hours standing at 5 C., 80 grams of urea are added to the mixture, which is heated to 25 C. and combined with 32 ml. of 0.5 N aqueous NaOH and 20 ml. of a 1 N aqueous KH P O, solution. The final mixture has a pH of 7.5.

Ten ml. of this substrate are combined with 2 ml. of the enzyme to be tested. After a reaction time of 10 minutes at 37 C., the reaction is terminated by adding 20 ml. of 0.3 N trichloroacetic acid solution. After minutes, the mixture is filtered. The filtrate, in a 10 mm. quartz cuvette, is measured at 280 pm. in a spectrophotometer against a control prepared in the same manner but in which the enzyme is first added after addition of the trichloroacetic acid.

At a measured extinction of 0.400,

EZA=l5,250/(enzyme weight in milligrams).]

To be sure, it is known in the art to employ papain for dehairing at a pH of 8. However, this known process does not offer the advantages of the process of the present invention. Further, it could not be foreseen from the use of this enzyme under alkaline conditions that dehairing would be possible in an acid region.

Good quality of the leather being prepared is assured only if acid swelling is avoided during the enzyme treatment. As known in the art, this can be achieved by adjusting the pH value with a desired acid, for example hydrochloric acid, and working in a sufficiently concentrated neutral salt solution. in a solution of sodium chloride, sodium sulfate, or ammonium sulfate, of a concentration of at least about 5 Baume, for example disadvantageous acid swelling no longer occurs. Acid swelling can also be avoided, as known in the art, by using socalled nonswelling acids for adjustment of the pH, for example naphthalene sulfonic acid, sulfophthalic acid, or oxyisobutyric acid. The use of such acids is discussed in detail in the art, for example in the article by G. Otto on pages 100-l06 ofDas Leder (1957), or in German Pat. No. 1,222,618.

The process can be practiced in such a manner that the hides and skins are immersed in a nonswelling enzyme bath. However, it is also possible first to treat the hides and skins in an enzyme-free, acid, nonswelling bath adjusted to a pH below 5, and then to take them out of the bath and to treat them from the flesh side with an enzyme preparation in powder or paste form.

In both processes, any kind of fungus or bacterial growth is impossible so that no preservatives need to be added. A further advantage of the process is that it leads to a complete destruction of pigmentation while extensively preserving the skin substance.

The process of the invention can advantageously be combined with oxidative dehairing, which also takes place in an acid region. For the dehairing of calf and goat skins, cowhide, pigskin and the like, a small residuum of hair often remains. This can be completely removed using about one third of the amount of sodium chlorite usually employed in the art for oxidative dehairing, whereby the grain is not attacked. [Oxidative dehairing processes are discussed in the article by K. Rosenbusch on pages 1 19-121 of Das Leder" 1964).]

The process of the present invention is shown in greater detail in the following examples, which are given by way of illustration and not intended to limit the scope of the invention.

In the examples, the weights of treating agent are expressed in percent by weight of the hides treated. Also, the EZA values for the pepsin used in examples 1, 5, and 7 were determined at a pH of 4; the EZA of the commercial enzyme product of example 6 was determined at pH 5. The procedure used was as described earlier, but employed a buffer system other than NaOHlKH Po EXAMPLE 1 One hundred kg. of dried Chinese goatskins were softened in the usual manner, preferably enzymatically. Dehairing followed paddling using 300 percent of water (run in at a temperature of 30 C.), 15 percent of sodium chloride, and 0.5 percent of pepsin (EZA=55,000). The skins were paddled in this bath for 30 minutes, whereupon 1.5 percent of hydrochloricv acid (32 percent technical grade, diluted 1:10) was slowly added.

The initial pH value of the bath was 3.0-3.3. The treatment time in the dehairing bath was 24 hours. After this period, the bath had a pH of 4.0-4.3.

The skins were subsequently dehaired in the usual fashion.

EXAMPLE 2 One hundred kg. of dried Chinese goatskins were thoroughly softened, preferably enzymatically. These skins were then paddled for 30 minutes with 300 percent of water (30 C. run-in temperature), 15 percent of sodium chloride, and 0.2 percent of papain (EZA=145,000). After thirty minutes paddling, 1.0 percent of hydrochloric acid (32 percent technical grade, diluted 1:10) were added and the skins were paddled for another 30 minutes.

The treatment time amounted to 24 hours. During this time, the hides were paddled 3 or 4 times for S-minute periods. Dehairing was subsequently accomplished in the usual way.

EXAMPLE 3 To kg. of dried Chinese goatskins were added 700 percent of water (30 C. run-in temperature), 1 percent of papain (EZA=30,000), and 3 percent of naphthalene sulfonic acid. The skins were briefly agitated initially. With increasing softening of the skins, agitation was increased. After 36 hours, the skins were dehaired.

EXAMPLE 4 One hundred grams of salted cowhides were paddled in the following manner: 350-400 percent of water (30 C. run-in temperature), 1 percent of papain (EZA=30,000), and 3 percent of a-oxy-isobutyric acid were added and initially agitated for 20 minutes. The treatment time amounted to 36 hours. During this time, the skins were paddled 3 or 4 times for 15-20-minute periods.

Subsequently, the skins were dehaired in the usual manner.

EXAMPLE 5 One hundred kg. of salted cowhides were softened overnight. Subsequent to the softening, enzymatic dehairing followed employing 100 percent of water (30 C. run-in temperature), 5 percent of sodium chlorine, and 0.5 percent of pepsin (EZA=60,000). The hides were agitated in this bath for minutes, after which 1.5 percent of hydrochloric acid (32 percent technical grade") was added, and then turned for a further 30 minutes. The skins remain in this bath for 20 to 22 hours. They were subsequently dehaired.

Further treatment of the hides followed in the same bath. Four percent of sodium chlorite was added thereto and the skins were piled overnight.

After this time, the opening of the hide is terminated and any residual hairs still present have been gelatinized. To determine whether free chlorine is still present in the bath, it is tested with potassium iodide-starch paper. If necessary, free chlorine is removed with sodium thiosulfate and the hides are treated further in the conventional manner diluted 1:10

EXAMPLE 6 One-hundred kg. of dried Chinese goatskins were thoroughly softened, preferably enzymatically. The following dehairing takes place in paddler using 300 percent of water (30 C. run-in temperature), 15 percent of sodium chloride, and 5 percent of an acid fungus tryptase available under the trade name Vernase (EZA= 5,000). These skins were first paddled for 30 minutes, after which 1 percent of hydrochloric acid (32 percent technical grade diluted 1:10) were added, and then paddled for a further 30 minutes. The treatment time amounted to 24 hours. To achieve a faultless loosening of the hair, it is advantageous to agitate 3 or 4 times for 5-minute periods. Subsequently, dehairing was carried out in the usual manner.

EXAMPLE 7 The process of example 1 was repeated except that an enzyme mixture comprising 0.3 percent of pepsin (EZA= 60,000) and 0.5 percent of a commercially available neutral bacterial protease were employed in place of 0.5 percent of pepsin. The bacterial protease comprised 15,000 Loehlein- Volhard units [cf. Gerbereichemisches Taschenbuch, by A. Kuentzel, Verlag Th. Steinkopff, Dresden and Leipzig 1955 86.]86.

The result was comparable to that of example 1.

EXAMPLE 8 Example 2 was repeated except that, in place of 0.2 percent of papain, an enzyme mixture comprising 0.15 percent of papain (EZA=145,000) and 1 percent of a commercially available neutral bacterial protease comprising 5,000 Loehlein-Volhard units was employed.

The result was the same as that in example 2.

EXAMPLE 9 Example 2 was repeated employing a mixture of 0.15 percent of papain (EZA=145,000) and 1 percent of a commercially available neutral mold fungus protease comprising 5,000 Loehlein-Volhard units, instead of 0.2 percent of papain.

The result was the same as that obtained in example 2.

What is claimed is:

1. ln a process for the enzymatic dehairing of skins and hides, the improvement wherein said skins and hides are treated for 24 to 48 hours at l5-40 C. under nonswelling conditions and at a pH less than 5 with an enzyme selected from the group consisting of pepsin, papain, a mold-fungus protease having an optimum effect at a pH less than 5, and mixtures thereof.

2, A process as in claim 1 wherein said skins and hides are treated at a pH between about 3 and about 5.

3. A process as in claim 1 wherein said enzyme is pepsin.

4. A process as in clai r n l wh rei n said enzyme is papain. 

2. A process as in claim 1 wherein said skins and hides are treated at a pH between about 3 and about
 5. 3. A process as in claim 1 wherein said enzyme is pepsin.
 4. A process as in claim 1 wherein said enzyme is papain. 